Electronic pacers (pacemakers) are used to artificially stimulate tissue such as the heart muscle with a pulsed electrical signal in order to correct or modify its rhythm. Body-implantable pacers are quite common, and generally comprise a small self-contained housing or can which encloses a source of electrical energy (a battery) and an electronic apparatus for producing electrical impulses at appropriate intervals. It is implanted by making a subcutaneous cavity in which the housing is positioned. The housing is made with a thin width to this end, so that it makes as small a bulge as possible on the overlying skin. An electrode at one end of a catheter is implanted in the heart muscle. The other end of the catheter has a lead formed thereon which is electrically coupled to the pacer pulse generator to complete the pacer circuit.
It is important that the catheter lead is safely secured to the pacer to prevent it from being inadvertently decoupled. Since pacers must often be removed and replaced as a complete unit without need of disturbing the electrode, the lead connection must also be readily disconnectable.
It has been common in the art to accomplish this connection by inserting an exposed terminal pin of the lead into an electrical terminal located at the inboard end of a cylindrical bore in the neck of the pacer, which may be a header formed on the pacer. The lead is then fixed in place by use of a setscrew, which extends through a tapped hole through the side of the header into the bore.
This conventional technique for securing the lead to the pacer has significant drawbacks. The manipulation of an extremely small screw through the use of a wrench or other tool can be difficult and time-consuming. Fairly elaborate steps must additionally be taken to secure the setscrew and seal the tapped hole of the setscrew against body fluids. To this end, surgical cement or some other sealing compound is typically introduced into the tapped hole to fix the set-screw in place and seal the hole. Furthermore, removal of the pacer is complicated by the need to remove the cement from the hole and setscrew.
Alternatives to the use of the foregoing setscrew technique have been developed, such as shown in U.S. Pat. Nos. 4,259,962 and 4,112,953, for example. These alternatives substantially rely upon the lead being tightly gripped within the bore by resilient strands, flanges and the like. The leads can be removed by exerting sufficient axial force to pull them out.
In the first instance, it is undesirable to have a surgeon yanking on a pacer lead to pull it out from the pacer, particularly when the electrode is embedded in the heart. This may also damage the lead as well as deform the coupling mechanism. Secondly, the lead may pull free from the pacer after implantation if sufficient force is applied which exceeds the strength of the connection.